JP5466862B2 - Ultrafine metal particle dispersed ink and method for producing the same - Google Patents

Description

  The present invention relates to an ultrafine metal particle-dispersed ink in which metal nanoparticles are dispersed in a vehicle and a method for producing the same.

  Ultrafine metal particle dispersed ink in which conductive fillers containing fine metal powders such as silver and copper are dispersed in a vehicle is called a polymer-type conductive ink (hereinafter simply referred to as “conductive ink”), a jumper circuit, It is used as a material for electromagnetic wave shields and touch panels. In particular, in the application of printed circuit patterns on circuit boards, the development of so-called “ultra-fine pattern” circuit formation technology using conductive ink in which “metal nanoparticles” are dispersed in response to higher wiring pattern density. It is being advanced.

  A vehicle is a highly viscous solution composed of an organic polymer resin and a solvent, and the metal nanoparticles tend to aggregate, so that it is difficult to uniformly disperse the metal nanoparticles in the vehicle. Among metals, copper is easily oxidized, so that it is particularly difficult to stably hold it in a solvent in a metallic state. Therefore, several methods for solving these problems have been proposed (Patent Documents 1, 2, etc.).

Japanese Patent Laid-Open No. 11-140511 JP 2008-88518 A JP 2000-340030 A JP-A-2005-340124

  However, even if copper nanoparticles with little aggregation are obtained, the conventional method for producing conductive ink in which copper nanoparticles are dispersed in a high-viscosity vehicle is likely to cause re-aggregation and poor dispersion during the production process. It is difficult to obtain uniformly dispersed copper nanoparticles. A general method for producing a conductive ink is by kneading and dispersing a metal powder and an auxiliary agent such as a dispersant and a leveling agent in a high-viscosity vehicle while applying a shearing force with a roll or a mixer. Here, when using “copper” nanoparticles as the metal fine powder, it is necessary to further improve the dispersibility. However, if the shearing force of the roll or mixer is increased, the copper nanoparticles are pressed and aggregated instead. .

  On the other hand, from the viewpoint of resistivity, it is said that in order to obtain sufficient performance as a conductive ink, it is necessary to fill at least 75% by mass of copper powder in the ink. However, the copper nanoparticles not only have a large surface area and volume but also have a poor affinity with the organic polymer resin, so that the higher the filling, the easier the aggregation.

  The present invention has been made in view of the circumstances unique to “copper nanoparticles” that tend to cause surface oxidation and aggregation as described above, and prevents the oxidation and aggregation of copper nanoparticles. The main technical problem is to obtain a metal ultrafine particle-dispersed ink that is highly filled with copper nanoparticles and that can maintain a uniformly dispersed state.

  The ultrafine metal particle dispersed ink according to the present invention includes a dispersion of copper nanoparticles having a primary particle diameter of 100 nm or less in a phenol resin solution, and each primary particle is coated with a phenol resin, It is characterized by being distributed and held. In addition, the magnitude | size of the primary particle diameter shown by this invention is defined as the average value which measured 100 particle | grains with the transmission electron microscope.

  In order to produce such a metal ultrafine particle dispersed ink, a small amount of phenol resin is first dissolved in an organic solvent. Next, copper hydroxide is stirred and dispersed in a solution of an organic solvent in which the phenol resin is dissolved, and finally a reducing agent is added to the dispersion obtained by stirring and dispersing the copper hydroxide so that the primary particle diameter is 100 nm or less. A phenol resin solution in which certain copper nanoparticles are uniformly dispersed is precipitated in the solution, and the precipitate is collected.

  According to the ultrafine metal particle-dispersed ink according to the present invention, copper nanoparticles can be uniformly dispersed in a phenol resin solution at a high concentration, and a fine conductive pattern having high conductivity can be formed. Further, since copper is much cheaper than silver or the like, there is an advantage in manufacturing cost.

It is process drawing which shows the procedure of the manufacturing method of the metal ultrafine particle dispersion ink which concerns on this invention.

-Manufacturing method of ultrafine metal particle dispersed ink-
FIG. 1 is a process diagram showing a procedure of a method for producing a metal ultrafine particle dispersed ink according to the present invention. As shown in this figure, the manufacturing method is roughly divided into three steps. Hereinafter, each step will be described.

[First step] (Solution adjustment step S1)
First, a solution of an organic solvent in which a small amount of a phenol resin is dissolved in an organic solvent is prepared in a reaction tank. The phenolic resin may be a resol type or a novolac type. However, the resol type phenol resin is preferable because it has high solubility in an organic solvent such as alcohol and acetone and does not require a curing agent. The organic solvent for dissolving the phenol resin is preferably an alcohol solvent from the viewpoint of safety and workability. Specific examples include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol.

  The phenol resin content in this solution is preferably in the range of about 0.5 to 15% by mass. The reason for this is that if the phenol resin content is less than 0.5% by mass, the amount of phenol resin is too small, so that the precipitated copper nanoparticles tend to aggregate together, while the phenol resin content in the solution is 15%. If it is larger than mass%, the surface of copper hydroxide is coated with a phenol resin and the reduction reaction tends to be hindered, so that a large amount of reducing agent is required and the reaction time becomes longer. The most preferable range is a range in which the phenol resin content is about 2 to 10% by mass.

[Second step] (copper hydroxide dispersion step S2)
Next, a dispersion solution of copper nanoparticles is generated by adding copper hydroxide to the solution obtained in the first step and stirring the solution. Copper hydroxide is an aggregate of nanoparticles and is insoluble in the solution prepared in the first step, but can be uniformly dispersed in the solution by stirring with a stirrer or the like.

[Third Step] (Copper Nanoparticle Reduction Separation Step S3)
By adding a reducing agent to the dispersion obtained in the second step, copper hydroxide is reduced to precipitate copper nanoparticles having a primary particle size of 100 nm or less. As soon as the copper nanoparticles begin to precipitate in the solution, the surrounding phenolic resin adsorbs to the copper nanoparticles, so the surface of the copper nanoparticles is coated with the phenolic resin, forming a monodispersed composite in the solution. To disperse. Furthermore, this composite becomes an aggregate having copper nanoparticles as a nucleus.

  When the reducing agent is added and then allowed to cool, a “phenol resin solution containing a large amount of copper nanoparticles” precipitates at the bottom of the reaction vessel. This precipitate is separated and collected. The obtained precipitate contains copper nanoparticles at a high concentration, but each copper nanoparticle is considered to be in a so-called “monodispersed state” having a uniform size and good dispersibility. Because the surface is coated with phenolic resin, no aggregation occurs.

  As the reducing agent, a common reducing agent such as sodium borohydride, formaldehyde, hydrazine and the like can be used. However, when hydrazine is used, the reaction time is short and the odor is small, which is preferable in terms of work efficiency. In order to shorten the reaction time, the dispersion of copper hydroxide to which the reducing agent is added is preferably set to 20 ° C. or higher in advance.

  If copper oxide or cuprous oxide is used instead of copper hydroxide in the second step, coarse particles having a primary particle diameter of about 500 nm of copper precipitated in the third step are generated. Similarly, when copper carbonate is used, it has been found that coarse particles having a primary particle diameter of precipitated copper exceeding 100 nm are generated. Since these have a large primary particle size, they are not preferable when used as conductive ink for ultrafine patterns.

(Embodiment)
Hereinafter, embodiments of the ultrafine metal particle dispersed ink according to the present invention will be described in more detail using a plurality of examples. The following examples are not to be construed as limiting.

<Example 1>
[First step]
A solution having a phenol resin content of 10% by mass in which 40 g of a resol type phenol resin is dissolved in 360 g of methyl alcohol is prepared, and the liquid temperature is set to about 20 ° C.

[Second step]
Add 50 g of copper hydroxide to the solution obtained in the first step and stir and disperse.

[Third step]
While stirring the copper hydroxide dispersion obtained in the second step, 100 ml of 80% hydrazine aqueous solution is added. After a while, copper nanoparticles precipitated, and the reaction stopped after 6 minutes. Thereafter, the reaction was allowed to cool for 2 hours after the reduction reaction was stopped, and the precipitated copper nanoparticle-containing phenol resin solution was recovered.

<Results of Example 1>
The obtained copper nanoparticle-containing phenol resin solution contained 78% by mass of copper nanoparticles having an average particle diameter of 30 nm in the phenol resin, and the copper nanoparticles were uniformly dispersed.

The copper nanoparticle-containing phenol resin solution was cured by heating at 170 ° C. for 15 minutes, and the coating film conductivity was measured. As a result, the resistivity was 1.2 × 10 ⁻³ Ω · cm, which was a performance that could be used as an ink for electromagnetic wave shielding coating.

<Example 2>
[First step]
A solution having a phenol resin content of 7% by mass in which 28 g of a resol type phenol resin is dissolved in 372 g of methyl alcohol is prepared, and the liquid temperature is set to 20 ° C.

[Second step]
Add 50 g of copper hydroxide to the solution obtained in the first step and stir and disperse.

[Third step]
While stirring the copper hydroxide dispersion obtained in the second step, 100 ml of 50% hydrazine aqueous solution is added. After a while, copper nanoparticles were precipitated and the reaction was stopped after 4 minutes. Thereafter, the reaction was allowed to cool for 2 hours after the reduction reaction was stopped, and the precipitated copper nanoparticle-containing phenol resin solution was recovered.

<Results of Example 2>
The obtained copper nanoparticle-containing phenol resin solution contained 82% by mass of copper nanoparticles having an average particle diameter of 40 nm in the phenol resin, and the copper nanoparticles were uniformly dispersed.

The copper nanoparticle-containing phenol resin solution was cured by heating at 170 ° C. for 15 minutes, and the coating film conductivity was measured. As a result, the resistivity was 3.7 × 10 ⁻⁴ Ω · cm, which was a performance that could be used as a conductive circuit ink.

<Example 3>
[First step]
A solution having a phenol resin content of 3% by mass in which 12 g of a resole type phenol resin is dissolved in 388 g of methyl alcohol is prepared, and the liquid temperature is set to 20 ° C.

[Second step]
Add 50 g of copper hydroxide to the solution obtained in the first step and stir and disperse.

[Third step]
When 100 ml of a 50% aqueous hydrazine solution was added while stirring the copper hydroxide dispersion obtained in the second step, copper nanoparticles started to precipitate immediately and the reaction was stopped after 3 minutes. Thereafter, the reaction was allowed to cool for 2 hours after the reduction reaction was stopped, and the precipitated copper nanoparticle-containing phenol resin solution was recovered.

<Results of Example 3>
The obtained copper nanoparticle containing phenol resin solution contained 90 mass% of copper nanoparticles having an average particle diameter of 40 nm in the phenol resin, and the copper nanoparticles were uniformly dispersed.

The copper nanoparticle-containing phenol resin solution was cured by heating at 170 ° C. for 15 minutes, and the coating film conductivity was measured. As a result, the resistivity was 1.0 × 10 ⁻⁴ Ω · cm, which was a performance that could be used as a conductive circuit ink.

<Example 4>
[First step]
A solution having a phenol resin content of 2% by mass in which 392 g of methyl alcohol is dissolved in 8 g of a resol type phenol resin is prepared, and the liquid temperature is set to 20 ° C.

[Second step]
Add 50 g of copper hydroxide to the solution obtained in the first step and stir and disperse.

[Third step]
While stirring the dispersion of copper hydroxide obtained in the second step, 100 ml of a 50% hydrazine aqueous solution was added, copper nanoparticles immediately started to precipitate, and the reaction was stopped after 3 minutes. Thereafter, the reaction was allowed to cool for 2 hours after the reduction reaction was stopped, and the precipitated copper nanoparticle-containing phenol resin solution was recovered.

<Results of Example 4>
The obtained copper nanoparticle containing phenol resin solution contained 92 mass% of copper nanoparticles having an average particle size of 40 nm in the phenol resin, and the copper nanoparticles were uniformly dispersed.

The copper nanoparticle-containing phenol resin solution was cured by heating at 170 ° C. for 15 minutes, and the coating film conductivity was measured. As a result, the resistivity was 8.0 × 10 ⁻⁵ Ω · cm, which was a performance that could be used as a conductive circuit ink.

<Example 5>
[First step]
A solution having a phenol resin content of 3% by mass in which 388 g of ethyl alcohol is dissolved in 388 g of ethyl alcohol is prepared, and the liquid temperature is set to 20 ° C.

[Second step]
Add 50 g of copper hydroxide to the solution obtained in the first step and stir and disperse.

[Third step]
When 100 ml of a 50% aqueous hydrazine solution was added while stirring the copper hydroxide dispersion obtained in the second step, copper nanoparticles started to precipitate immediately and the reaction was stopped after 3 minutes. Thereafter, the reaction was allowed to cool for 2 hours after the reduction reaction was stopped, and the precipitated copper nanoparticle-containing phenol resin solution was recovered.

<Results of Example 5>
The obtained copper nanoparticle-containing phenol resin solution contained 90% by mass of copper nanoparticles having an average particle diameter of 15 nm in the phenol resin, and the copper nanoparticles were uniformly dispersed.

The copper nanoparticle-containing phenol resin solution was cured by heating at 170 ° C. for 15 minutes, and the coating film conductivity was measured. As a result, the resistivity was 8.7 × 10 ⁻⁵ Ω · cm, which was a performance that could be used as a conductive circuit ink.

[Table 1] List of experimental conditions and experimental results

(Summary)
According to the results of Examples 1 to 5, all of the obtained copper nanoparticle-containing phenol resin solutions were uniformly dispersed with a content of 78% by mass or more of copper nanoparticles having an average particle size of 40 nm or less in the phenol resin. It was confirmed that In addition, the conductivity of the coating film was in the order of resistivity minus 10 or less, and it was confirmed that the conductivity was extremely high. In particular, in the copper resin-containing phenol resin solution obtained as a result of Example 5, copper nanoparticles having an average particle size of 15 nm are uniformly dispersed in the phenol resin at a content of 90% by mass, and the resistivity of the coating film is Since it was 8.7 × 10 ⁻⁵ Ω · cm, it had excellent characteristics sufficient as a conductive ink for ultra-fine patterns and the like.

  Therefore, based on this copper nanoparticle-containing phenol resin solution, by finely adjusting the resin composition, solvent, auxiliaries, etc. according to the intended printing conditions, it is easy to meet printability and performance after coating and drying. A conductive ink excellent in conductivity can be produced. In addition, the conventional process of kneading and dispersing copper nanoparticles in a high-viscosity vehicle is not required, so that it can be manufactured at a lower cost and in a shorter time than the conventional one. Furthermore, since all the copper nanoparticles are handled in the solution, there is an advantage that dangers such as dust explosion due to scattering of copper nanoparticles and toxicity to the human body due to suction can be avoided.

  The metal ultrafine particle-dispersed ink according to the present invention can be used for high-density printed circuits with ultrafine patterns, and can be used for drawing fine line widths such as jumper circuits and touch panels because there is no migration problem. In addition, it can be used as ink for ink jet printing, and thus the industrial applicability is very large.

S1 Solution adjustment step S2 Copper hydroxide dispersion step S3 Copper nanoparticle reduction separation step

Claims (4)

The resol type phenol resin solution contains a dispersion of copper nanoparticles whose primary particle diameter is 100 nm or less, each primary particle is coated with a resol type phenol resin, and is uniformly dispersed in the resol type phenol resin solution. An ultra-fine metal particle dispersed ink characterized by being dispersed and held in A step (S1) of dissolving a phenol resin in an organic solvent;
A step (S2) of stirring and dispersing copper hydroxide in a solution of an organic solvent in which the phenol resin is dissolved;
Adding a reducing agent to the dispersion obtained by stirring and dispersing the copper hydroxide to precipitate a phenol resin solution in which copper nanoparticles having a primary particle diameter of 100 nm or less are uniformly dispersed in the solution (S3); ,
A method for producing a metal ultrafine particle dispersed ink comprising:   The method for producing ultrafine metal particle dispersed ink according to claim 2, wherein the organic solvent is alcohol.   The method for producing an ultrafine metal particle-dispersed ink according to claim 2, wherein the content of the phenol resin is 0.5 to 15% by mass.

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